Technical Field
The present invention relates to an organic light emitting diode, and more particularly, to an organic light emitting diode having a high quantum efficiency (light emission efficiency) and a narrow full width at half maximum, and an organic light emitting display device including the same.
Discussion of the Related Art
Recently, as display devices become large in size, a demand for flat display elements occupying a small space increases, and a technology of an organic light emitting display device including an organic light emitting diode (OLED) as one out of the flat display elements has been developed rapidly.
The OLED is an element where when an electrode and a hole are injected to an emitting material layer formed between an electron injection electrode (cathode) and a hole injection electrode (anode), an electrode-hole pair is generated then disappears to emit a light.
The OLED is able to be formed on a flexible transparent substrate such as a plastic, is able to be operated at a low voltage (e.g., below 10V), is relatively low in a power consumption, and is excellent in colors.
The OLED includes a first electrode on a substrate, a second electrode facing and spaced apart from the first electrode, and an organic light emitting layer between the first and second electrodes. For example, the first electrode may be an anode, and the second electrode may be a cathode.
To improve a light emission efficiency, the organic light emitting layer may include a hole injection layer (HIL), a hole transporting layer (HTL), an emitting material layer (EML), an electron transporting layer (ETL) and an electron injection layer (ETL) that are sequentially stacked on the first electrode.
A hole moves from the first electrode as an anode to the emitting material layer through the hole injection layer and the hole transporting layer, and an electrode moves from the second electrode as a cathode to the emitting material layer through the electron injection layer and the electron transporting layer.
The hole and electron moving to the emitting material layer are combined and form an exciton, which is excited to an unstable energy state and then returns to a stable energy state to emit a light.
An emitting material used for the emitting material layer may be broadly categorized into a fluorescent material and a phosphorescent material.
When the exciton is formed by combining the hole and the electron, a singlet exciton and a triplet exciton are formed at a ratio of 1:3. In case of the phosphorescent material, both of the singlet exciton and the triplet exciton are involved in light emission, and thus the OLED including the emitting material layer of the phosphorescent material has a high light emission efficiency.
However, the phosphorescent emission has limits to an iridium (Ir) complex design, which should use an Ir complex, and to a blue emission.
The fluorescent material has a less limit to a dopant and is applicable to a blue emission. However, in the fluorescent material, only a singlet exciton is involved to a light emission while the triplet exciton of the remaining 75% is not involved to a light emission. Accordingly, the OLED including the emitting material layer of the fluorescent material has a low quantum efficiency.